using System;

public class Program

{

    public static void Main()

    {

        long n = 600851475143;

        int d = 0;

        int nd = 0;

        int max = 0;

        for (int factor = 5; factor < Math.Sqrt(n); factor +=2 )

        {

            if ( n % factor == 0 )

            {

                for( d=1; d<=Math.Sqrt(factor); d++ )

                {

                    if(factor%d==0)

                    {

                        nd ++;

                    }

                }

                if ( nd == 1 )

                {

                    max = factor;

                }

                nd = 0 ;

            }

        }

        Console.WriteLine(max);

    }

}